"What do you get the man who has everything for his birthday?" asked the commentator.

Easy. An Oscar.

Jose Mourinho celebrated his 51st birthday with a 1-0 victory over Stoke City in the FA Cup on Sunday thanks to a sublime free-kick from Brazilian midfielder Oscar.

Coming in the 27th minute, Chelsea had failed to test Stoke goalkeeper Asmir Begovic up to that point, although the Bosnian stood little chance with Oscar's effort from 20 yards that nestled in the far left corner.

It proved to be the decisive moment in the game—as fitting a strike as any to settle a game—although Chelsea should have ran out far more comfortable winners than the scoreline suggests.

Eden Hazard's good form continued, causing Stoke problems throughout the game, but it was Oscar who stood out as Chelsea's finest performer—his display a stark reminder as to why Juan Mata was allowed to leave to join Manchester United for £37.1 million this week.

Indeed, with Chelsea fans still licking their wounds over Mata's move north to their rivals, Oscar's excellent performance couldn't have come at a better time.

The Brazilian controlled the game at Stamford Bridge, with everything good and positive the Blues produced going through him.

He could have scored more than his one goal, striking the post near the end of the first half, while almost assisting Frank Lampard, who just failed to connect with his cross.

Ian Walton/Getty Images

For any team to lose a talent such as Mata, it's going to significantly dent their hopes of winning major honors. If Oscar's form continues like this, however, it could very much be a case of business as usual for Chelsea with the Premier League and others firmly set within their sights.

Sunday wasn't a game in isolation. It represented the norm at Stamford Bridge, something Chelsea fans and the rest of the Premier League have come to expect from Oscar.

The 22-year-old is the focal point of Mourinho's Chelsea. He is the sum of its parts. Without him, this Chelsea team simply isn't the same proposition.

Ian Walton/Getty Images

And with Hazard outside of Oscar on the left flank, it's clear why Mourinho felt the need to cash in on Mata when he had the chance.

We saw that on Sunday. In fact, we've seen for much of 2013-14, and as the season continues, we will continue to see it.

"It's a bit of a contradiction because we played so well but we won with a free-kick," Mourinho said, per ChelseaFC.com. "Normally when you play this well you win by scoring some amazing goals from open play."

Mourinho added, "We played a very good game again: the 1-0 doesn't reflect the quality of our game and the dominance of our game."

It's unfortunate for Mata—a player who gave so much in his two-and-a-half years in West London—but this Chelsea team evolved around him in a way that meant the Spaniard had become surplus given the nature of the team Mourinho is creating.

At the very heart of it is Oscar. Sunday reminded us of that.

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Chelsea's reward for defeating Stoke City is a trip to Etihad Stadium, where they will face Manchester City in the fifth round of the FA Cup. The tie will be played over the weekend of Feb. 15/16.

Garry Hayes is Bleacher Report's lead Chelsea correspondent and will be following the club from a London base throughout the 2013-14 season. Follow him on Twitter here @garryhayes